ICOS and acute myeloid leukemia: Well-beyond investigating the expression of isolated molecules, our study aims to simultaneously evaluate the B7 checkpoint ligand phenotype of AML blasts (B7.1, B7.2, PD-L1, PD-L2, ICOS-L, B7-H3, B7-H4) and the expression of immune checkpoint receptors (ICRs) [inducible T cell costimulator (ICOS), PD-1, CTLA-4] on helper and cytotoxic T cell maturation populations and to correlate these data to standard prognostic factors.